The Role of Neurotransmitters in Mood and Motivation

Here I will describe the basic relationships between mood, motivation, and neurotransmitters as an extension of the model of mood and motivation offered in my first post to this blog.  I will not offer many links to research on well-established phenomena, such as the role of 5-HT serontonin in mood.

5-HT serotonin is the proxy for mood in my models.  It is the neurotransmitter reponsible for the negatively- accelerated curve that represents mood-related net motivation and feelings of positive affect.  This involves the relationship between objective and subjective weights on gains and losses in the risk-averse(80% of people) genotypes.  Incidentally, risk neutral curves are linear and risk-seeking positively hyperbolicly accelerating. 

As previously mentioned, the subjective values of both gains and losses increase as serotonin decreases, and this effect is reflected in the changes that occur in dopaminergic activity.  More specifically, there is an inverse relationship between serotonergic and dopaminergic activity.  As dopamine is well-established as the facilitating neuromodulator of arousal, the Yerkes-Dodson law demonstrates the relationship between dopamine functioning and net motivation(task performance) with some precision. Hence, the relationship between serotonin and dopamine as it relates to motivation is also well-established. 

It should also be noted that this relationship also underlies increased severity of negative emotional responses when dopamine is increased without antecedant increases in serotonin.  This is witnessed in those who consume stimulants such as cocaine, but can be attenuated at times by the increases in serotonin, in a reverse of the typical cause/effect relationship.  When negative affect is triggered in this case, emotional responses such as anger will sometimes lead to violent expression.  The effect of relative dopamine levels or genotypic sensitivity can be modeled by the addition of a multiplier to the equation for net motivation(call it "d").

To move onto the roles of other neurotransmitters, opiods are proxies for gains, with decreased arousal; decreased GABA for losses for fear/anxiety(expected risks/losses), with concomitant increased arousal(dopamine).

It is by now clear what the roles of the above neurotransmitters are and how they interact to determine mood and motivation.  Effects on specific emotional responses will be addressed in a later post.